The present invention relates to variable valve mechanisms of internal combustion engines.
Intake valve throttle control systems, in general, control the flow of gas and air into the cylinders of an engine by varying the timing, duration and/or lift (i.e., the valve lift profile) of the intake valve(s) in response to engine operating parameters, such as, for example, engine load, speed and driver input. Intake valve throttle control systems vary the valve lift profile through the use of various mechanical, electro-mechanical and/or electro-hydraulic configurations, generally referred to herein as variable valve mechanisms. Examples of variable valve mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference.
Conventional variable valve mechanisms are associated with the cam or input shaft of an engine. More particularly, conventional variable valve mechanisms typically include components which are mounted onto the input or cam shaft and undergo pivotal or rotational movement relative thereto. The components of a conventional variable valve mechanism are typically slid onto and over the camshaft into a desired position thereon. The components are dimensioned to closely receive the camshaft to thereby enable smooth and reliable pivotal and/or rotational movement relative thereto.
In a multi-cylinder engine, the camshaft extends the entire length of the engine cylinder head and includes at least one cam lobe for each cylinder. The cam lobes are spaced along the length of the camshaft, and transfer rotary motion of the cam or input shaft to a respective variable valve mechanism. The cam lobes are typically formed integrally with the cam shaft, such as by machining. At least a portion of the cam lobes extend outside the diameter of the input or cam shaft. Thus, the components of a conventional variable valve mechanism which are slidingly received over and mounted onto the camshaft can not be slid past the point where the first cam lobe is positioned on the camshaft. The enlarged-diameter cam lobe precludes sliding components beyond the cam lobe. Therefore, in multi-cylinder engines having conventional variable valve mechanisms, the camshaft must be segmented into multiple sections. Each of the multiple sections corresponds to a respective cylinder of the engine.
Segmentation of the camshaft permits components of the variable valve mechanism to be slid into position on either side of the cam lobe. Further, segmentation of the camshaft enables variable valve mechanisms to be installed for each cylinder. However, segmentation of the camshaft increases the number of machining operations required and thus increases machining costs. Further, the segmented camshafts of each cylinder require precise alignment relative to each other. The alignment process is time-consuming, labor intensive and costly.
Conventional variable valve mechanisms typically include many component parts, such as link arms, joints, pins and return springs, and are thus relatively complex mechanically. The many component parts increase the cost of the mechanism and make the mechanism more difficult to assemble and manufacture. The joints and pins of a conventional variable valve mechanism are subject to interfacial frictional forces which negatively impact durability and efficiency. The use of return springs negatively impact the durability and limit the operating range of conventional variable valve mechanisms, thereby limiting the operation of the intake valve throttle control system to a correspondingly-limited range of engine operation.
Therefore, what is needed in the art is a variable valve mechanism having a one-piece, unitary camshaft.
Furthermore, what is needed in the art is a variable valve mechanism having fewer component parts.
Still further, what is needed in the art is a variable valve mechanism with fewer joints and/or pins.
Moreover, what is needed in the art is a variable valve mechanism that eliminates the use of return springs.
The present invention provides a variable valve mechanism for an internal combustion engine.
The invention comprises, in one form thereof, an elongate input shaft having a central axis. An opening cam lobe and a closing cam lobe are disposed upon the input shaft. The opening cam lobe and the closing cam lobe are in a predetermined angular relationship relative to each other and relative to the central axis. A rocker assembly has a first end and a second end. The rocker assembly carries a roller that engages the opening cam lobe. A first split frame member assembly is pivotally mounted upon the input shaft. The first split frame member assembly is pivotally coupled at a first end thereof to the rocker assembly. The first split frame is configured for being pivotally coupled at a second end thereof to a control shaft. A first split output cam is pivotally mounted upon the input shaft, and a link pivotally couples the first split output cam to the second end of the rocker assembly.
An advantage of the present invention is that the one-piece unitary cam or input shaft eliminates the need to precisely align multiple, segmented camshafts.
Another advantage of the present invention is that it uses fewer component parts relative to a conventional variable valve mechanism, thereby reducing the cost and complexity of the mechanism.
A further advantage of the present invention is that fewer joints/pins are necessary relative to a conventional variable valve mechanism, thereby reducing friction and increasing durability of the mechanism.
A still further advantage of the present invention is that return springs are not required, thereby further increasing the durability of the mechanism and enabling use of the mechanism over a wider range of engine operating conditions.